Chemically amplified resist compositions

ABSTRACT

Provided is a chemically amplified resist composition comprising a photoacid generator and an acid sensitive resin which has a huge molecular weight and from which the dissolution controlling group is cleaved owing to the decomposition of the partially crosslinked structure by the acid released from the photoacid generator. By the above-described composition, ultrafine processing can be carried out with improved focal depth, whereby an excellent rectangular pattern can be formed.

The present Application is a Divisional Application of U.S. patentapplication Ser. No. 09/573,009, filed on May 18, 2000 now U.S. Pat. No.6,342,334.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a chemically amplified resist composition andmore specifically, to a chemically amplified resist composition improvedin the depth of focus.

2. Description of the Prior Art

In the fields of the fabrication of various devices typified by asemiconductor device, which require fine processing on the order ofsubmicrons, there is an increasing demand for actualizing higherdensification and higher integration. Under such situations, therequirements for photolithography have become severer.

In recent days, a chemically amplified resist attracts attentions insuch fields. This chemically amplified resist makes use of the catalyticaction of an acid formed by exposure to light. It is characterized inthat since the generation efficiency of an acid is high even under theconditions providing only small exposure energy, it has high sensitivityand high resolution.

The resist is composed principally of a photoacid generator whichreleases an acid and an acid sensitive resin which undergoes a markedchange in the solubility in an aqueous alkaline solution, which is adeveloper, owing to the generation of the acid.

As an example of the prior art, a chemically amplified resistcomposition comprising, as an photoacid generator,N-(p-toluenesulfonyloxy)-5-norbornene-2,3-dicarboxyimide and, as an acidsensitive resin, a (hydroxystyrene)-(tert-butylcarboxystyrene) copolymercan be mentioned.

When the above-described resist is exposed to light, first-stagereaction occurs in accordance with the below-described reaction scheme(6), whereby N-(p-toluenesulfonyloxy)-5-norbornene-2,3-dicarboxyimideused as a photoacid generator is decomposed and p-toluenesulfonic acid(p-toluenesulfonic acid ion) which is an acid component, is released.

Then, in the second-stage reaction, the acid thus released acts on theacid sensitive resin, that is, a(hydroxystyrene)-(tert-butylcarboxystyrene) copolymer, whereby the acidsensitive resin is converted into an alkali-soluble(hydroxystyrene)-(tert-carboxystyrene) copolymer in accordance with thebelow-described reaction scheme (7). This alkali-soluble resin isdissolved in an alkali developer, whereby development is effected.

The alkali development is allowed to proceed through the reactionprocedures as described above. Owing to a high generation efficiency ofan acid in exposed regions, a pattern of high resolution is available.

Owing to the recent tendency to higher densification and higherintegration, it has come to be impossible to sufficiently satisfy therequest for ultra-fine processing of a device even by using such aresist.

For example, when the above-described resist was applied to a siliconsubstrate, followed by exposure to light and development by a KrFstepper under the optical conditions of NA of 0.60 and σ of 0.75 to forma contact hole pattern of 0.20 μm, the depth of focus thus obtained wasonly 0.60 μm. It was therefore difficult to form a contact hole having asufficient rectangularity.

On the surface of a wafer, there exists unevenness due to innercircuits. When a resist is applied onto such unevenness, this unevennessis reproduced to some extent on the surface of the resist. In this case,best focus is not always available all over the wafer. The depth offocus, which is a focus margin, must be sufficiently deep for ultra-fineprocessing even in such a case.

In FIG. 2, an inner circuit 22, an intrastratum insulating film 23 and aresist layer 24 are formed over a substrate 21. This drawing illustrateshow the resist layer 24 is exposed to light for the formation of acontact hole in the intrastratum insulating film 23, on the suppositionthat a substrate wafer is exposed to light at three places by moving thestage having the substrate wafer placed thereon.

The resist layer 24 reproduces, on its surface, unevenness of the innercircuits. In this case, a distance between the light source for exposureand the resist layer is not always constant on the whole surface of thewafer. Moreover, the light intensity upon exposure has a predetermineddistribution. For example, in spite of the best focus at the site (2),the sites (1) and (3) are under the state of defocus and the intensityof the light incident on the resist inevitably becomes weak. When aconventional resist is employed, exposure is insufficient at the site ofweak light intensity, leading to a marked reduction in resolution.

A description was so far made of the lowering in the resolution due toshortage in the light intensity upon exposure. In addition, a filmdecrease upon alkali development becomes one factor for disturbingultrafine processing.

FIG. 3 is a schematic view illustrating the etching of the intrastratuminsulating film 32 with a resist pattern formed over the intrastratuminsulating film 32 laid over the substrate 31. In FIGS. 3(b-1) to3(b-3), an ordinarily employed resist 33 b is used. As is apparent fromFIG. 3(b-2), a developer causes a film decrease of the resist 33 b,which prevents the formation of a good rectangular pattern. When theintrastratum insulating film is etched using this pattern, the narrowingof the intrastratum insulating film occurs. This pattern is thereforenot suited for ultrafine processing.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide a chemicallyamplified resist composition which permits ultrafine processing improvedin the depth of focus and is excellent in the pattern rectangularity, inconsideration of the above-described problems.

In a first aspect of the present invention, there is thus provided achemically amplified resist composition comprising an photoacidgenerator which releases an acid by exposure to light and an acidsensitive resin which has an alkali soluble group protected with adissolution controlling group and is converted into an alkali solubleresin by the cleavage of the dissolution controlling group caused by theaction of the acid, wherein the acid contains a sulfonic acid group anda carboxyl group and the alkali soluble resin contains a carboxyl group.

In the above-described chemically amplified resist composition, thephotoacid generator is preferably a compound represented by thefollowing formula (1):

R¹(CO)₂N—OSO₂—R²—COOC(CH₃)₃  (1)

wherein R¹ represents a dicarboxyimide compound residue and R²represents a cyclohexylene or phenylene group.

In the above-described chemically amplified resist composition, the acidsensitive resin is preferably represented by the below-described formula(2) or (3) and has a weight-average molecular weight of 3,000 to 30,000:

wherein R³ represents a tert-butyl group, tetrahydropyranyl group orR⁴(R⁵O)CH— in which R⁴ and R⁵ each independently represents a C₁₋₄ alkylgroup, x stands for 0.4 to 0.9 and y stands for 0.1 to 0.9.

In the above-described chemically amplified resist composition, thephotoacid generator is incorporated in an amount of 1 to 15 wt. %relative to the acid sensitive resin.

In a second aspect of the present invention, there is also provided achemically amplified resist composition comprising an photoacidgenerator which releases an acid by exposure to light, and an acidsensitive resin which has an alkali soluble group protected with adissolution controlling group and is converted into an alkali solubleresin by the cleavage of the dissolution controlling group caused by theaction of the acid, wherein the acid sensitive resin is represented bythe below-described formula (4) or (5) and has a weight-averagemolecular weight of 100,000 to 5,000,000:

wherein R⁶ represents a crosslinked structure of —O— C(CH₃)₂—O— or—CO—O—C(CH₃)₂—O—CO—, R⁸ represents a hydroxyl group or a carboxyl group,z stands for 0.1 to 0.9 and w stands for 0.1 to 0.9.

In the chemically amplified resist composition, when the crosslinkedstructure R⁶ of the acid sensitive resin is —CO—O—C(CH₃)₂—O—CO—, thephotoacid generator is preferably a compound represented by thefollowing formula (1):

 R¹(CO)₂N—OSO₂—R²—COOC(CH₃)₃  (1)

wherein R¹ represents a dicarboxyimide compound residue and R²represents a cyclohexylene or phenylene group.

In the chemically amplified resist composition, the photoacid generatoris incorporated in an amount of 1 to 15 wt. % relative to the acidsensitive resin.

The chemically amplified resist composition according to the firstaspect of the present invention comprising a photoacid generator whichreleases, by exposure to light, an acid containing both a sulfonic acidgroup and a carboxyl group; and an acid sensitive resin which undergoescleavage of a dissolution controlling group by the action of the acid toform an alkali soluble resin containing a carboxyl group has aremarkably improved maximum dissolution rate and also improved focusdepth by the association of the sulfonic-acid-containing acid with thealkali soluble resin in an alkali developer.

The chemically amplified resist composition according to the secondaspect of the present invention comprises a photoacid generator and anacid sensitive resin which has a huge molecular weight and from whichthe dissolution controlling group is cleaved by the decomposition of thepartial crosslinked structure due to the acid released from thephotoacid generator. This chemically amplified resist has a sufficientmolecular weight at unexposed regions, which makes it possible to lowerthe minimum dissolution rate and to form a good rectangular pattern,thereby improving the depth of focus.

Moreover, by using, in combination, the photoacid generator whichreleases an acid containing both a sulfonic acid group and a carboxylgroup by exposure to light, and an acid sensitive resin which forms acarboxyl-containing alkali soluble resin by the decomposition of itspartial crosslinked structure caused by the acid, it is possible tosimultaneously accomplish an increase of the maximum dissolution rateand decrease of the minimum dissolution rate, whereby the excellentfocal depth is available.

Use of such a chemically amplified resist composition having a deepfocal depth makes it possible to conduct ultrafine processing such asformation of a contact hole of 0.20 μm or less or formation of a circuithaving a line spacing or line width of 0.15 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a log-log graph illustrating the relationship between theexposure energy of a resist and dissolution rate; FIG. 2 illustrates howthe resist having unevenness on its surface is exposed to light, whereinindicated at numeral 21 is a substrate, 22 an inner circuit, 23 anintrastratum insulating film and 24 a resist layer; FIG. 3 is aschematic view for describing the rectangularity by comparing resistpatterns formed using resists different in the maximum dissolution rate,wherein indicated at numeral 31 is a substrate, 32 an intrastratuminsulating film, 33 a a resist layer having a small minimum dissolutionrate and 33 b a resist layer (conventional resist) having an ordinaryminimum dissolution rate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present inventors paid particular attentions to the solubility of aresist in an alkali. FIG. 1 is a log-log graph illustrating therelationship between the exposure energy of the resist and dissolutionrate. As illustrated in this drawing, at smaller exposure energy, thedissolution rate is low and shows the minimum fixed value (minimumdissolution rate), indicating difficulty in development at the sitewhere exposure is blocked by a mask or the like. The dissolution ratestarts a drastic increase at the exposure energy increased to a certainvalue. By a further increase in the exposure energy, the dissolutionrate shows the maximum fixed value (maximum dissolution rate). Thismaximum dissolution rate indicates easiness of development at the maskopening site.

When the exposure properties of a resist as shown in FIG. 1 are takeninto consideration, there are two methods to attain an improvement inthe focal depth, which is an object of the present invention. The firstone is to raise the maximum dissolution rate while substantiallymaintaining the minimum dissolution rate.

Described specifically, an improvement in the maximum dissolution rateenables a sufficient dissolution rate even at a site where the intensityof light is low, which makes it possible to attain sufficient resolutionat a defocus site, such as the site (1) or (3) in FIG. 2, where theintensity of an incident light on the resist is weak.

The second method is to lower the minimum dissolution rate whilesubstantially maintaining the maximum dissolution rate. Describedspecifically, in this method, a film decrease in an alkali developer issuppressed by controlling the solubility of the unexposed site of theresist in an alkali developer.

FIGS. 3(a-1) to (a-3) are schematic views illustrating how theintrastratum insulating film 32 is etched when the resist 33 a having asmall minimum dissolution rate is employed.

Since the minimum dissolution rate of the resist is suppressed to alower level, a film decrease does not occur easily at an unexposedportion of a resist pattern as shown in FIG. 3(a-1), which is differentfrom that shown in FIG. 3(b-1). Thus, a good rectangular pattern withexcellent focal density is formed. Favorable patterning free fromnarrowing can be conducted by etching of the intrastratum insulatingfilm through the resulting pattern.

As described above, an improvement in the focal depth of a resist, whichis an object of the present invention, can be attained and sufficientresolution is available even in ultra fine processing, by raising themaximum dissolution rate of the resist, lowering its minimum dissolutionrate, or adopting both measures. The maximum dissolution rate or minimumdissolution rate to be raised or lowered varies depending on the kind ofa light source employed.

First, a description will next be made of the composition of a resistfor attaining the first method. A chemically amplified resistcomposition is formed of, as essential ingredients, a photoacidgenerator which releases an acid by exposure to light and an acidsensitive resin which is converted to an alkali soluble resin by theacid thus released.

The photoacid generator employed in the first method of the presentinvention must release an acid containing therein both a sulfonic acidgroup and a carboxyl group when exposed to light. Any photoacidgenerator can be used in the present invention insofar as it satisfiesthe above-described condition and releases an acid with sufficientlyhigh efficiency by exposure to light.

Examples of such a compound include compounds each represented by thefollowing formula (1):

R¹(CO)₂N—OSO₂—R²—COOC(CH₃)₃  (1)

wherein R¹ represents a dicarboxyimide compound residue and R²represents a cyclohexylene or phenylene group.

Specific examples includeN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimide,N-(p-tert-butylcarboxybenzenesulfonyloxy)-phthalimide,N-(p-tert-butylcarboxybenzenesulfonyloxy)-naphthalimide,N-(p-tert-butylcarboxycyclohexylsulfonyloxy)-5-norbornene-2,3-dicarboxyimide,N-(p-tert-butylcarboxycyclohexylsulfonyloxy)-phthalimide andN-(p-tert-butylcarboxycyclohexylsulfonyloxy)-naphthalimide. The chemicalformulas of the above-exemplified compounds are shown in Table 1.

TABLE 1 Chemical formula Name

N-(p-tert- butylcarboxybenzene- sulfonyloxy)-5-norbornene-2,3-dicarboxyimide

N-(p-tert-butylcarboxy- benzenesulfonyloxy)- phthalimide

N-(p-tert-butylcarboxy- benzenesulfonyloxy)- naphthalimide

N-(p-tert-butylcarboxy- cyclohexylsulfonyloxy)-5- norbornene-2,3-dicarboxyimide

N-(p-tert-butylcarboxy- cyclohexylsulfonyloxy)- phthalimide

N-(p-tert-butylcarboxy- cyclohexylsulfonyloxy)- naphthalimide

As the acid sensitive resin, usable is a resin which contains an alkalisoluble group protected with a dissolution controlling group and isconverted into a carboxyl-containing alkali soluble resin by cleavage ofthe dissolution controlling group owing to the action of the acidreleased from the photoacid generator.

Examples of such an acid sensitive resin include resins each having aweight-average molecular weight of 3,000 to 30,000 and represented bythe below-described formula (2) or (3):

wherein, R³ represents a tert-butyl group, a tetrahydropyranyl group orR⁴(R⁵O)CH— in which R⁴ and R⁵ each independently represents a C₁₋₄ alkylgroup, x stands for 0.4 to 0.9, preferably 0.5 to 0.75, more preferably0.55 to 0.65 and y stands for 0.1 to 0.9.

Use of such a photoacid generator and an acid sensitive resin incombination brings about a marked improvement in the maximum dissolutionrate of an exposed portion in an alkali developer, because the carboxylgroup of the acid released from the photoacid generator associates, inan alkali developer, with the carboxyl group of the alkali soluble resinformed by the cleavage of the dissolution controlling group from theacid sensitive resin. As a result, the alkali soluble resin acquires asulfonic acid group, thereby having notably improved affinity with thealkali developer.

For example, whenN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimideand (hydroxystyrene)_(m)-(p-tert-butylcarboxystyrene)_(n) correspondingto a KrF light source are used as a photoacid generator and an acidsensitive resin, respectively, the photoacid generator is converted, byexposure to light, into p-tert-carboxybenzenesulfonic acid(p-tert-carboxybenzenesulfonic acid ion) in accordance with the reactionscheme (8).

The resulting acid causes a reaction to remove the dissolutioncontrolling group (tert-butyl group) from the acid sensitive resin inaccordance with the reaction scheme (7), whereby an alkali soluble resin(hydroxystyrene)_(m)-(p-carboxystyrene)_(n) is formed.

Since this (hydroxystyrene)_(m)-(p-carboxystyrene)_(n) contains acarboxyl group, it smoothly associates withp-tert-carboxybenzenesulfonic acid in an alkali developer as shown inthe formula (9).

As a result, owing to the action of a sulfonic acid group, the affinityof the alkali soluble resin with the alkali developer shows a remarkableimprovement, leading to a rise in its maximum dissolution rate.

Also in the case where (carboxytetracyclododecyl methacrylate)_(m)-(tert-butylcarboxytetracyclododecyl methacrylate)_(n) is used, forexample, as the resin corresponding to an ArF light source, itassociates with p-tert-carboxybenzenesulfonic acid in an alkalideveloper as shown in the reaction scheme (10), which heightens themaximum dissolution rate.

A description will next be made of the composition of the resist forattaining the second method of the present invention. Similar to theresist used in the first method, the chemically amplified resistcomposition in this second method comprises, as essential ingredients, aphotoacid generator which releases an acid by exposure to light and anacid sensitive resin which is converted into an alkali soluble resin bythe acid thus released.

In this method, the acid sensitive resin has, in the molecule thereof, apartial crosslinked structure for lowering the minimum dissolution rate.

More specifically, the acid sensitive resin has a weight-averagemolecular weight of 100,000 to 5,000,000 and is represented by thebelow-described formula (4) or (5):

wherein, R⁶ represents —O—C(CH₃)₂—O— or —CO—O—C(CH₃)₂—O—CO—, R⁸represents a hydroxyl or carboxyl group, z stands for 0.1 to 0.9 and wstands for 0.1 to 0.9. This resin will hereinafter be calledcrosslink-structured resin.

Next, the reaction mechanism upon exposure will be described using, asan example, an acid sensitive resin which is a resin corresponding to aKrf light source and has a hydroxystyrene skeleton and has, as acrosslinked structure, an isopropylideneoxy group (—O—C(CH₃)₂—O—). Theisopropylidene group, which is a dissolution controlling group, iscleaved by the acid as shown in the reaction scheme (11), whereby theacid sensitive resin is converted into an alkali soluble resin.

When a resin having a carboxytetracyclododecyl methacrylate skeleton isused as a resin corresponding to an ArF light source, an alkali solubleresin is formed, as shown in the reaction scheme (12), by the reactionmechanism similar to that shown in the reaction scheme (11).

In either case, the acid sensitive resin having a weight-averagemolecular weight of 100,000 to 5,000,000 is sparingly soluble in analkali developer at an unexposed portion, which makes it possible tosufficiently lower the minimum dissolution rate. On the other hand, thecrosslinked portion forming a giant molecule is cleaved by exposure tolight, which largely lowers the molecular weight during the process toform an alkali soluble resin, while maintaining the maximum dissolutionrate at a similar level to that of the conventional resist composition.When the crosslinked structure R⁶ represents —CO—O—C(CH₃)₂—O—CO— in theformula (4) or (5) of the acid sensitive resin, it is preferred to usethe photoacid generator of the first method and releases an acidcontaining both a sulfonic acid group and a carboxyl group by exposureto light, because when the crosslinked structure CO—O—C(CH₃)₂—O—CO— iscleaved by the action of an acid as shown in the reaction scheme (13),the alkali soluble resin thus formed contains a carboxyl group.

Such a resist composition is effective both for lowering the minimumdissolution rate and raising the maximum dissolution rate.

In the chemically amplified resist composition according to the presentinvention, the photoacid generator is incorporated in an amount of 1 to15 wt. %, preferably 5 to 10 wt. % relative to the acid sensitive resin.

In the chemically amplified resist composition according to the presentinvention, a solvent is used in order to dissolve therein the photoacidgenerator and acid sensitive resin. As preferred solvents, PGMEA(propylene glycol monomethyl ether acetate) and EL (ethyl lactate) canbe used. For example, PGMEA is used singly for a resin corresponding toa KrF light source, while a 1:1 mixed solvent of PGMEA and EL is usedfor a resin corresponding to an ArF light source.

The acid sensitive resin is preferably incorporated in an amount ofabout 11 to 21 wt. % based on the whole resist solution and the solventis preferably added in an amount of about 79 to 89 wt. % based on thewhole resist solution.

It is possible to add, to the chemically amplified resist of the presentinvention, known additives such as tackifier, leveling agent andanti-foaming agent within an extent not damaging the characteristics ofthe present invention.

As a preferred example of the alkali developer usable for the chemicallyamplified resist composition of the present invention, an aqueoussolution containing TMAH (tetramethoxyammonium hydroxide) represented bythe formula (14) can be mentioned. For example, a 2.38% TMAH aqueoussolution can be used for the development of a resin corresponding to anKrF light source, while a 0.12% TMAH aqueous solution can be used forthe development of a resin corresponding to an ArF light source.

EXAMPLES Example 1

As an acid sensitive resin, a resin represented by the formula (2)wherein R³ represents a tert-butyl group and x stands for 0.57 andhaving a weight-average molecular weight of 15,000 was employed.

A resist composition comprising 16 wt. % of the acid sensitive resin,1.6 wt. % (10 wt. % of the acid sensitive resin) ofN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimideas a photoacid generator and 82.4 wt. % of PGMEA as a solvent wasapplied to a silicon substrate to form a film having a thickness of 0.70μm. The resulting film was then exposed to light by a KrF stepper underthe optical conditions of NA of 0.60 and σ of 0.75, whereby a contacthole pattern of 0.20 μm was formed. As an alkali developer, a 2.38% TMAHaqueous solution was employed.

Based on the cross-sectional observation of the pattern formed afterdevelopment, the depth of focus was evaluated.

Upon alkali development, the maximum dissolution rate and the minimumdissolution rate were evaluated at varied exposure energies by using aresist dissolution rate measuring apparatus manufactured by Perkin-Elmercorporation.

As a result, it was found that the composition had excellent focal depthof 1.00 μm, a maximum dissolution rate as high as 1.0 μm/s, and aminimum dissolution rate of 10⁻⁵ μm/s which was substantially the sameas that of the ordinarily-employed resist composition corresponding toan KrF light source.

Comparative Example 1

A resist composition comprising 16 wt. % of the acid sensitive resinemployed in Example 1, 1.6 wt. % (10 wt. % of the acid sensitive resin)of N-(p-toluenesulfonyloxy)-5-norbornene-2,3-dicarboxyimide as aphotoacid generator and 82.4 wt. % of PGMEA as a solvent was applied toa silicon substrate to form a film having a thickness of 0.70 μm. Theresulting film was then exposed to light by a KrF stepper under theoptical conditions of NA of 0.60 and σ of 0.75, whereby a contact holepattern of 0.20 μm was formed. As an alkali developer, a 2.38% TMAHaqueous solution was employed.

As a result of the evaluation under the utterly same conditions as thosein Example 1, the composition was found to have a focal depth as shallowas 0.60 μm, a maximum dissolution rate of 0.3 μm/s, and a minimumdissolution rate of 10⁻⁵ μm/s.

Example 2

As an acid sensitive resin, employed was a crosslink-structured resinrepresented by the formula (4) wherein R⁶ represents —O—C(CH₃)₂—O— and zstands for 0.5 and having a weight-average molecular weight of3,000,000.

A resist composition comprising 17 wt. % of the acid sensitive resin,1.7 wt. % (10 wt. % of the acid sensitive resin) ofN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimideas a photoacid generator and 81.3 wt. % of PGMEA as a solvent wasapplied to a silicon substrate to form a film having a thickness of 0.50μm. The resulting film was then exposed to light by a KrF stepper underthe optical conditions of NA of 0.60 and σ of 0.75, whereby a stripepattern having a line spacing and line width, each 0.18 μm was formed.As an alkali developer, a 2.38% TMAH aqueous solution was employed.

As a result of the evaluation under the utterly same conditions as thoseof Example 1, it was found that the composition had excellent focaldepth of 0.80 μm and a maximum dissolution rate as high as 1.0 μm/s. Itwas also found that the composition had a minimum dissolution rate of10⁻⁶ μm/s, which was smaller than that of the ordinarily-employed resistcorresponding to a KrF light source. The rectangularity of the patternwas excellent.

Comparative Example 2

In a similar manner to Example 2, film formation, pattern formation andevaluation were carried out using the resist composition employed inComparative Example 1.

As a result, the composition was found to have a focal depth as shallowas 0.50 μm, a maximum dissolution rate of 0.3 μm/s, and a minimumdissolution rate of 10⁻⁵ μm/s.

In addition, the cross-sectional observation revealed the occurrence ofa film decrease.

Example 3

As an acid sensitive resin, a resin represented by the formula (3)wherein R³ represents a tert-butyl group and y stands for 0.60 andhaving a weight-average molecular weight of 12,000 was employed.

A resist composition comprising 17 wt. % of the acid sensitive resin,0.85 wt. % (5 wt. % of the acid sensitive resin) ofN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimideas a photoacid generator and 82.15 wt. % of a 1:1 mixed solvent of PGMEAand EL as a solvent was applied to a silicon substrate to form a filmhaving a thickness of 0.70 μm. The resulting film was then exposed tolight by an ArF Stepper under the optical conditions of NA of 0.60 and σof 0.75, whereby a contact hole pattern of 0.2 μm was formed. As analkali developer, a 0.12% TMAH aqueous solution was employed.

As a result of the evaluation under the utterly same conditions as thoseof Example 1, it was found that the composition had excellent focaldepth of 0.60 μm and a maximum dissolution rate as high as 0.08 μm/s.These values are much superior to those of the ordinarily employedresist corresponding to an ArF light source. It was also found that aminimum dissolution rate was 10⁻³ μm/s, which was almost equal to thatof the ordinarily-employed resist corresponding to an ArF light source.

Comparative Example 3

A resist composition comprising 15 wt. % of the acid sensitive resinemployed in Example 3, 0.75 wt. % (5 wt. % of the acid sensitive resin)of N-(p-toluenesulfonyloxy)-5-norbornene-2,3-dicarboxyimide as aphotoacid generator and 84.25 wt. % of a 1:1 mixed solvent of PGMEA andEL as a solvent was applied to a silicon substrate to form a film havinga thickness of 0.70 μm. The resulting film was then exposed to light byan ArF stepper under the optical conditions of NA of 0.60 and σ of 0.75,whereby a contact hole pattern of 0.20 μm was formed. As an alkalideveloper, a 0.12% TMAH aqueous solution was employed.

As a result of the evaluation under the utterly same conditions as thosein Example 1, the composition was found to have a focal depth as shallowas 0.30 μm, a maximum dissolution rate of 0.02 μm/s, and a minimumdissolution rate of 10⁻³ μm/s.

Example 4

As an acid sensitive resin, employed was a crosslink-structured resinrepresented by the formula (5) wherein the cross-linked structure R⁶represents —CO—O—C(CH₃)₂—O—CO— and w stands for 0.4 and having aweight-average molecular weight of 4,000,000.

A resist composition comprising 16 wt. % of the acid sensitive resin,0.8 wt. % (5 wt. % of the acid sensitive resin) ofN-(p-toluenesulfonyloxy)-5-norbornene-2,3-dicarboxyimide as a photoacidgenerator and 83.2 wt. % of a 1:1 mixed solvent of PGMEA and EL as asolvent was applied to a silicon substrate to form a film having athickness of 0.50 μm. The resulting film was then exposed to light by aKrF stepper under the optical conditions of NA of 0.60 and a of 0.75,whereby a stripe pattern having a line spacing and line width, each 0.15μm, was formed. As an alkali developer, a 0.12% TMAH aqueous solutionwas employed.

As a result of the evaluation under the utterly same conditions as thoseof Example 1, it was found that the composition had excellent focaldepth of 1.00 μm, a maximum dissolution rate of 0.02 μm/s, which wasequal to that of the ordinarily employed resist corresponding to an ArFlight source, and a minimum dissolution rate of 10⁻⁴ μm/s, which wassmaller than that of the ordinarily-employed resist corresponding to anArF light source. In addition, the rectangularity of the pattern wasexcellent.

Comparative Example 4

In a similar manner to Example 4, film formation, pattern formation andevaluation were carried out using the resist composition employed inComparative Example 3.

As a result, the composition was found to have a focal depth as shallowas 0.50 μm, a maximum dissolution rate of 0.02 μm/s, and a minimumdissolution rate of 10⁻³ μm/s.

In addition, the cross-sectional observation revealed the occurrence ofa film decrease.

Example 5

A resist composition comprising 17 wt. % of the acid sensitive resinemployed in Example 4, 0.85 wt. % (5 wt. % of the acid sensitive resin)ofN-(p-tert-butylcarboxybenzenesulfonyloxy)-5-norbornene-2,3-dicarboxyimideas a photoacid generator and 82.15 wt. % of a 1:1 mixed solvent of PGMEAand EL as a solvent was applied to a silicon substrate to form a filmhaving a thickness of 0.50 μm. The resulting film was then exposed tolight by a KrF stepper under the optical conditions of NA of 0.60 and σof 0.75, whereby a stripe pattern having a line spacing and line width,each 0.15 μm, was formed. As an alkali developer, a 0.12% TMAH aqueoussolution was employed.

As a result of the evaluation under the utterly same conditions as thoseof Example 1, it was found that the composition had excellent focaldepth of 1.10 μm, a maximum dissolution rate of 0.08 μm/s, which wasequal to that of the ordinarily employed resist corresponding to an ArFlight source, and a minimum dissolution rate of 10⁻⁴ μm/s, which wassmaller than that of the ordinarily-employed resist corresponding to anArF light source. In addition, the rectangularity of the pattern wasexcellent.

It should be noted that in the present invention, the weight-averagemolecular weight is a value as measured by liquid chromatography (interms of styrene).

What is claimed is:
 1. A chemically amplified resist compositioncomprising an photoacid generator which releases an acid by exposure tolight, and an acid sensitive resin which has an alkali soluble groupprotected with a dissolution controlling group and is converted into analkali soluble resin by the cleavage of the dissolution controllinggroup by the action of the acid, wherein said acid sensitive resin hasweight-average molecular weight of 100,000 to 5,000,000 and representedby the following formula (4) or (5):

wherein R⁶ represents a crosslinked structure of —O—C(CH₃)₂—O— or—CO—O—C(CH₃)₂—O—CO—, R⁸ represents a hydroxyl group or a carboxyl group,z stands for 0.1 to 0.9 and w stands for 0.1 to 0.9.
 2. A chemicallyamplified resist composition according to claim 1, wherein when thecrosslinked structure R⁶ is —CO—O—C(CH₃)₂—O—CO—, the photoacid generatoris a compound represented by the following formula (1):R¹(CO)₂N—OSO₂—R²—COOC(CH₃)₃  (1) wherein R¹ represents a dicarboxyimidecompound residue and R² represents a cyclohexylene or phenylene group.3. A chemically amplified resist composition according to claim 2,wherein the photoacid generator is incorporated in an amount of 1 to 15wt. % relative to the acid sensitive resin.
 4. A chemically amplifiedresist composition according to claim 1, wherein the photoacid generatoris incorporated in an amount of 1 to 15 wt. % relative to the acidsensitive resin.